This description relates to notifications for ambient dangerous situations.
Bicyclist and pedestrian safety, especially in urban areas, is highly dependent on the attentiveness of vehicle drivers. Unfortunately, in practice, many accidents or other dangerous situations occur because drivers are either unaware of, or are not focused on, bicyclists and pedestrians, owing to various distractions while driving or to inconvenient “blind spots”. Moreover, drivers, bicyclists, and pedestrians (that is, anyone on foot whether walking, running, or standing still) may themselves be distracted and be unaware of an impending accident or other dangerous situation involving another vehicle. The differences in speeds of travel, physical sizes, and degrees of protection from injury afforded between vehicles and people on foot or bicycles may make dangerous situations more prevalent and the injures more significant in collisions between people on foot or bicycles and other vehicles.
For example, an all-too-common phenomenon that endangers bicyclists, especially in urban areas, is “dooring”. When a driver parks their car on the side of a road that's shared with bicyclists, they may open the door without looking at whether a bicyclist is nearby and hit the bicyclist causing them to fall and get injured. In certain dire situations, which unfortunately do occur in practice, the bicyclist may get thrown into the path of vehicular traffic, leading to significant injuries or even death. The number of such incidents is significant; for instance, a study estimated 344 such incidents in Chicago alone in 2011 (Doorings in Chicago and NYC are still a sorry state but one of them is doing something about it. http://gridchicago.com/2012/doorings-in-chicago-and-nyc-are-still-a-sorry-state-but-one-of-them-is-doing-something-about-it/). It is likely that thousands of such incidents occur around the world each month.
Other examples of accidents or other dangerous situations involving vehicles and bicyclists or pedestrians are at intersections, pedestrian crossings (whether marked or not), and when cars attempt to pass bicyclists or pedestrians.